Letter: Current account

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The Independent Culture
Sir: Keith Bailey (letter, 11 August) asks why houses are not built with a 6-volt electrical supply as well as the normal 240-volt one. The reason is that it is impossible to transmit any significant amount of power over a distance of more than a few feet at 6 volts, unless cables of enormous size are used.

All wiring offers some resistance to the passage of current, and thus some power is lost in just pushing current to where it is wanted. The amount of power lost in this way depends on the square of the current, and so for a given amount of power to be delivered, the power lost in 6-volt transmission is 1,600 times that of 240-volt transmission. For that reason, 6-volt power supplies have to be produced by transforming down from mains voltage immediately adjacent to where they are needed.